81 x 9 = 801. What must you do to make the this equation true?

There are 2 people near the river and both of them want to get on the other side. The boat can only take one of them. But they got across.
How?

Can you count the number of triangles in the given figure?

I have branches, but no fruit, trunk or leaves. What am I?

Chef Andrea has to light the kitchen stoves to open her restaurant for the day. There are three stoves in the kitchen: A glass stove, a brick stove, and a wood stove. She only has one match. Which does she light up first?

Look at this sequence from top to bottom. What is the next number in the sequence?
1
11
21
1211
111221
312211

In the Chess Board picture below white army is arranged. You need to add a black army on the board such that no piece is under any threat.
Note: Army comprised of 1 king, 1 queen, 2 rooks, 2 bishops, 2 knights, and 8 pawns.

I am under you when I am whole.
I shift above you if you remove the first letter.
I come all around you if you remove the second as well.

Can you tell me who I am?

An express train takes 3 seconds to enter the tunnel which is 1 km long.
If it is travelling at 120 km an hour, how long will it take to pass completely through the tunnel?

What does below rebus means ?